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The average marks obtained in a test by x students of a class was m.

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The average marks obtained in a test by x students of a class was m.  [#permalink]

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New post 03 Jul 2017, 05:00
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A
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C
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Difficulty:

  85% (hard)

Question Stats:

35% (02:23) correct 65% (02:44) wrong based on 37 sessions

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The average marks obtained in a test by x students of a class was m. Was (x + 3) the average marks obtained by three students with the lowest marks in the same test?

(1) If the lowest three marks were excluded, the average score of the class would have increased by three.
(2) m = 2x.

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Re: The average marks obtained in a test by x students of a class was m.  [#permalink]

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New post 09 Jul 2017, 07:02
1
Bunuel wrote:
The average marks obtained in a test by x students of a class was m. Was (x + 3) the average marks obtained by three students with the lowest marks in the same test?

(1) If the lowest three marks were excluded, the average score of the class would have increased by three.
(2) m = 2x.


C ?

My understanding:

B doesnt help.

Using A:
say Sum of All/No Of Students=A/x=m
So A=mx.
Say Sum of lowest 3=L.
\frac{A-L}{x-3}=m+3
A-L=(x-3)(m+3)
A-L=mx+3x-3m-9
Use A=mx and change sides
L=3m-3x+9
L is sum of lowest 3, its average will be L/3=(3m-3x+9)/3= m-x+3
m could be anything, so Not sufficient.

Using m=2x from B,
L/3=2x-x+3=x+3
Sufficient. DS answer C.


BUT I believe if C is the answer then there might be some kind of trap making A/B/E the answer. :P
Couldn't find the trap.
Waiting for OA and OE by expert!
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Re: The average marks obtained in a test by x students of a class was m.  [#permalink]

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New post 09 Jul 2017, 07:29
1
C??

From 1 we can get that average marks obtained by three students with the lowest marks in the same test = (m-x)+3.

We have no Information about the relation between m&x and it may or may not be the case that m-x = x

2 doesn't help individually.

Combining 1 & 2 we get Average marks obtained by three students with the lowest marks in the same test = (m-x)+3 = (2x-x)+3 = x+3.

Hence C should be the answer.
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Re: The average marks obtained in a test by x students of a class was m.  [#permalink]

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New post 18 Jul 2017, 09:14
1
Bunuel wrote:
The average marks obtained in a test by x students of a class was m. Was (x + 3) the average marks obtained by three students with the lowest marks in the same test?

(1) If the lowest three marks were excluded, the average score of the class would have increased by three.
(2) m = 2x.


Average = \(\frac{Sum}{Number}\) = \(\frac{S}{x}\) = m
\(\frac{L}{3}\) = x+3?

1) Lowest 3 marks = L
\(\frac{(S-L)}{(x-3)}\) = x+3
=> S-L = mx+3x-3m-9
=> mx - L = mx+3x-3m-9
=> L = 3m-3x+9
\(\frac{L}{3}\) = m-x+3
m = ?
Insufficient.

2) m = 2x
Doesn't help. Insufficient.

1+2)
\(\frac{L}{3}\) = 2x-x+3 = x+3
Sufficient. C is the answer.
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Re: The average marks obtained in a test by x students of a class was m.   [#permalink] 18 Jul 2017, 09:14
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